That kind of contactless power transmission apparatus is broadly divided into a power transmitter in a primary side and a power receiver in a secondary side. The power transmitter includes a primary coil and is used for a device such as a charger or the like (hereinafter referred to as a “primary device”). The power receiver includes a secondary coil and is used for a device such as a cordless phone, a shaver, an electric toothbrush, a personal digital assistance or the like (hereinafter referred to as a “secondary device”). The primary and secondary coils constitute a transformer, and electric power is transmitted from the primary side to the secondary side by electromagnetic induction between the coils. Thus, the contactless power transmission apparatus does not have any electric contact for transmitting power from the primary side to the secondary side. Accordingly, the issue of contact degradation is not raised, and it is possible to easily pair the primary and secondary devices to transmit power from the primary side to the secondary side. In addition, each waterproof structure of the primary and secondary devices can be easily realized.
Each of the power transmitter and the power receiver further has a core or a bobbin (molding) in general, and each coil of them is wound around its core or bobbin.
In recent years, such a secondary device has been especially required to be miniaturized, thinned and provided with high performance. In order to comply with the requirement, the secondary coil needs to be thinned. Because of this, a planar coil has been proposed for the secondary coil (e.g., Japanese Patent Application Publication Number 2006-311712 published on Nov. 9, 2006). However, the planar coil is inferior in magnetic properties to the coil wound around a core, and accordingly power in the secondary side is reduced. If a magnetic layer is added to the planar coil, the power transmission efficiency between the primary and secondary sides can be enhanced, but a thin magnetic layer must be formed, which becomes a problem.
Also in order to miniaturize the secondary device, some parts in the secondary device are arranged to approach the planar coil and the distance among them is shortened. Accordingly, if the parts include a weak part in heat and noise, e.g., a lithium ion secondary battery or the like, the weak part is put under the influence of heat and noise, increased by proximity to the planar coil.